Sediment factories and the index of sediment generation

Sediment generation, a vital process connecting the Earth’s spheres, is highly heterogeneous in space and time. A major obstacle to deciphering its patterns and mechanisms has been the absence of robust quantitative proxies for regional-scale comparison. Here, we overcome this limitation by proposing a dimensionless Index of Sediment Generation (ISG), defined as the ratio of the suspended-load-flux proportion of a sub-catchment to its drainage-area proportion, which minimizes the impact of interannual variability and anthropogenic biases. By applying the ISG to data from 686 hydrological stations, we map regional sediment yield and define “ sediment factories” as localized zones of disproportionately intense erosion that supply a major fraction of a river's sediment load. Our analysis identifies sediment factories clustered around the Himalaya and Tibetan Plateau margins in Asia and in the upper Amazon River. Covering only 8.9% (0.84 million km²) of the monitored basin area, Asian factories generate ∼3,240 Mt of suspended sediment per year, representing 75% of the monitored flux to the ocean. We identify three types of sediment factories: first cycle (crystalline bedrock), recycled (erodible sediments/sedimentary rocks), and composite. The sediment factory concept pinpoints critical nodes in Earth surface dynamics, intrinsically linked to orogeny, weathering, carbon cycling, geohazards, and water-resources management.